The present application claims priority under 35 U.S.C. xc2xa7119 of German Patent Application No. 199 35 481.2, filed on Jul. 28, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to a process and device for producing a fibrous material web, in particular a paper or cardboard web, in which the fibrous material web is appropriately treated for the purpose of influencing certain web characteristics such as, in particular, the web structure and/or the fiber orientation.
2. Discussion of Background Information
It is known that, in the current conventional processes for producing fibrous material webs such as, in particular, paper webs, a more or less clear orientation of the fibers in the machine direction occurs. The average fiber orientation can be varied within certain boundaries dependent upon the operating characteristics of the sheet forming unit, i.e., dependent upon whether an overdamming or an underdamming is present, and upon the forces in the machine, in which situation the average fiber orientation defined by the sheet forming unit can only be changed in the direction of a greater longitudinal orientation, e.g., by means of forces in the press section.
It is further known that the edges of a fibrous material web shrink more than the web center in a conventional drying method. Different sheet characteristics across the web width result from this.
In a process known from U.S. Pat. No. 3,301,173, the elasticity of a belt is used to influence web characteristics in that the relatively dry web is compressed by the belt such that a microcreping of the web occurs with a corresponding change in thickness. In this process, the deformation of the belt thus primarily results in a thickness/length variation. However, besides the desired increase in flexibility and energy absorption, such as compression and/or microcreping of the relatively dry web always causes a significant loss in tensile strength in the lengthwise direction of the fibrous material web because some of the fibers are broken.
An aspect of the invention is to create a process and a device of the kind mentioned at the outset in which the aforementioned disadvantages are eliminated. This should particularly also create the possibility of, on the one hand, influencing and preferably increasing the degree of orientation of the fibers crosswise to the operating direction of the machine and, on the other hand, deliberately influencing the structure of the fibrous material web, in a simple and reliable manner.
This aspect is attained with regard to the process in that, in order to influence the applicable web characteristics, the fibrous material web is correspondingly stretched in the crosswise direction while still damp.
Because of this construction, it is now possible, on the one hand, to influence and preferably increase the orientation of the fibers crosswise to the operating direction of the machine and, on the other hand, to deliberately influence the structure of the fibrous material web, which also allows a deliberate influence across the width of the web, if necessary. With a deliberate crosswise stretching of the fibrous material web, the breaking length ratio is decreased as well. During tightening, the elastic belt furthermore behaves similarly to a web in a drying section, i.e., the edges behave differently from the middle of the web because of the different edge conditions. As a result, the contraction of the belt is also different across the width, which has the effect that the web edges are stretched more than the middle of the web. This effect works against an increased edge shrinkage of the web in the drying section and compensates partially or completely therefor. With the crosswise stretching of the fibrous material web, different characteristics of the web, e.g., a paper web, can be influenced, if necessary, also deliberately across the web width.
Among the characteristics of the fibrous material web that can be correspondingly influenced are, e.g., the porosity that can be increased as a result of a loosening of the structure, the smoothness or the smoothness profile, the strengths in the crosswise direction, and the stretching characteristics in the lengthwise direction. The open porosity achieved can, for example, improve the press performance and/or the drying performance. Furthermore, a better or more even acceptance of glue can also be achieved, for example.
The still-wet fibrous material web is suitably stretched in the crosswise direction with a solids content of around 5% to around 65%, in particular of around 5% to around 55%, and preferably of around 15% to around 25%.
In a preferred practical embodiment of the process according to the invention, the fibrous material web is transferred in its still-wet state onto an endless elastic belt which was stretched in the lengthwise direction before the transfer point and whose stretching behavior is adjusted in various directions such that, with the preceding lengthwise stretching of the belt, a crosswise contraction of the belt corresponding to the lengthwise contraction of the belt occurring after the transfer point primarily causes a crosswise stretching of the belt and the fibrous material web is stretched in the crosswise direction thereby.
It is advantageous in this situation for the stretching behavior of the elastic belt to be adjusted separately in the thickness and width direction in such a way that, with a lengthwise stretching or lengthwise contraction of the belt, at least essentially only a crosswise contraction of the belt and/or crosswise stretching of the belt occurs without significant changes in thickness. In comparison to the variation in thickness that has been common up to now, the fibers in the fibrous material web are thus no longer contracted, but rather reoriented. The preceding stretching of the elastic belt in the lengthwise direction suitably follows immediately before the transfer point.
The lengthwise stretching of the belt before receiving the fibrous material web can occur in different ways. In a suitable practical embodiment, the elastic belt is tensed by at least one driven rotating roll, and especially at least two rotating rolls driven in opposite directions and thus stretched in the lengthwise direction. The fibrous material web is preferably transferred to the elastic belt in the region of this one roll and/or the last of these rolls.
The transfer of the still-wet fibrous material web to the elastic belt suitably occurs at a solids content of the web of around 5% to around 65% weight, in particular of around 5% to around 55% weight, and preferably of around 15% to around 25% weight.
Additionally, besides the function of a crosswise stretching of the fibrous material web, the elastic belt can also fulfill one or more further functions. Thus, a belt serving at the same time as a pressing felt can be used as an elastic belt. It is fundamentally also possible to use a belt that is simultaneously serving as a transfer belt as an elastic belt. Such combinations have the advantage that only a few new machine components are necessary.
In a suitable embodiment, an elastic belt with a stretching behavior that varies across the web width is used, by which means different effects can be achieved, such as, e.g., the previously mentioned effect of a decreased edge shrinkage behavior of the web. As needed, an elastic belt with a closed surface or a porous elastic belt can be used.
In a suitable practical embodiment, the fibrous material web is transferred to the elastic belt by a transport belt such as, in particular, a wet wire, a transfer belt, or the like.
The device according to the invention is correspondingly characterized in that it includes a device for stretching the fibrous material web for the purpose of influencing certain web characteristics such as, in particular, the web structure and/or the fiber orientation in the crosswise direction in the still-wet state.
According to an aspect of the present invention a process is provided for influencing web characteristic in a machine for producing a fibrous web, the process including guiding the fibrous material web in a still-wet state; stretching the still-wet state fibrous material web in a crosswise direction.
According to another aspect of the present invention, the web characteristic includes at least one web structure and fiber orientation. In another aspect of the present invention the fibrous material web includes one of paper and cardboard.
According to a further aspect of the present invention, when stretched, the still-wet fibrous material has a solids content of about 5% to about 65%. Moreover, when stretched, the still-wet fibrous material web has a solids content of about 5% to about 55%; in particular about 5% to about 55%, and preferably around 15% to 25%.
In another aspect of the present invention, the process includes stretching a continuous elastic belt in a lengthwise direction before a transfer point, in which a cross-wise direction contraction results, transferring the fibrous material web onto the lengthwise stretched continuous elastic belt at the transfer point, and lengthwise contracting the continuous elastic belt after the transfer point, in which a cross-wise direction expansion results. In this manner, the fibrous material web is stretched in the crosswise direction.
According to a still further aspect of the present invention a process is provided wherein a stretching behavior of the elastic belt is such that the stretching and contracting in the lengthwise direction substantially effects the cross-wise direction contracting and expansion without significantly changing a thickness of the elastic belt.
Further aspects of the invention provide a process wherein the elastic belt is stretched in a longitudinal direction immediately before the transfer point. According to other aspects of the present invention the stretching of the continuous elastic belt is effected by at least one driven rotating roll.
According to another aspect of the present invention the stretching of the continuous elastic belt is effected by at least two driven rolls rotating in opposite directions. According to an aspect of the invention the fibrous material web is transferred to the elastic belt in a region of a last roll used for stretching.
In another aspect of the present invention, the still-wet state fibrous material web is transferred to the elastic belt with a solids content of about 5% to about 65%; in particular about 5% to about 55%; and preferably about 15% to about 25%.
According to a further aspect of the present invention the continuous elastic belt includes a pressing felt. In another aspect of the present invention the continuous elastic belt includes a transfer belt. According to a further aspect of the present invention the continuous elastic belt has a stretching behavior that varies across the web width.
In another aspect of the present invention the elastic belt has a closed surface. According to still a further aspect of the present invention the elastic belt is porous. According to still a further aspect of the present invention the fibrous material web is transferred to the elastic belt from a transport belt comprising one of a wet wire and a transfer belt.
Further aspects of the invention include stretching the fibrous material web in the crosswise direction increases the degree of orientation of the fibers in the crosswise direction. According to other aspects of the present invention the stretching of the fibrous material web in the crosswise direction influences the structure of the fibrous material web is provided.
According to another aspect of the present invention an apparatus is provided for producing a fibrous material web. The apparatus includes a stretching device arranged to stretch the fibrous material web in a still wet state in a direction crosswise to a travel direction.
According to a further aspect of the present invention an apparatus is provided including wherein the stretching device is adapted to influence at least one of web structure and fiber orientation in the fibrous material web. According to a still further aspect of the invention the fibrous material web includes one of a paper and cardboard.
According to an aspect of the present invention, the apparatus includes an elastic belt positioned to receive the still-wet state fibrous material web at a transfer point. The elastic belt is stretched in a lengthwise direction before the transfer point, in which a crosswise contraction of the elastic belt can result, and the elastic belt is contractible after the transfer point, in which the crosswise stretching of the elastic belt can result. In this manner, the fibrous material web is stretched in the crosswise direction.
According to another aspect of the invention a stretching behavior of the elastic belt is such that the stretching and contracting in the lengthwise direction substantially effects the cross-wise direction contracting and expansion without significantly changing the thickness.
In another aspect of the present invention, an apparatus is provided including a driven rotating roll arranged to stretch the elastic belt in the lengthwise direction, wherein the elastic belt is tensed around said driven rotating roll.
According to a further aspect of the present invention the transfer point is located in a region of the driven roll. According to a still further aspect of the present invention, the elastic belt comprises a pressing felt. Further aspects of the invention include an elastic belt that includes a transfer belt.
According to other aspects of the invention, the apparatus has an elastic belt having a stretching behavior that varies across a width of the web. According to another aspect of the present invention the elastic belt has a closed surface. According to a further aspect of the present invention the elastic belt is porous.
According to another aspect of the present invention an apparatus is provided having a transport belt arranged to guide the fibrous web before the transfer point, wherein the fibrous material web is transferred to the elastic belt from a transport belt. In another aspect of the present invention the transfer belt comprises a wet wire.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.